Production of lightfast jute



FIP83 ABSTRACT OF THE DISCLOSUM Lightfast jute fabrics may be produced by (a) bleaching the jute fabric at a pH below 3.0 and at a temperature from about 60 F. to about 110 F. in an aqueous bleaching solution containing potassium permanganate and phosphoric acid in amounts such that the ratio of potassium permanganate to phosphoric acid is in the range between about 1:0.7 to about 1:1.1, and then (b) scavenging the bleached jute fabric with an aqueous solution of an inorganic reducing agent, such as sodium bisulfite, at a pH below 4.0, after which the fabric is scoured with hot water or steam. Using this process, it is possible to produce lightfast jute fabrics having a colorfastness equal to not less than Standard Fastness Hours, and in most instances between and Standard Fastness Hours, as determined by AATCC Standard Test Method 16A1963= This invention relates to jute and, more particularly, to techniques for bleaching jute fabrics. The invention provides an improved process for the production of lightfast jute, as well as a lightfast jute fabric having a colorfastness which is appreciably greater than that of any other jute fabric bleached by conventional techniques.

Jute fibers or strands are produced from the stems of two species of the herbaceous annual plant Corchorus, both of which species are distinguishable only by their seed pods and seeds. Both the round-pod jute (Corchorus capsular-is) and the long-pod jute (Corchorus olitorius) are extensively cultivated in India and Pakistan, jute being the most important bast fiber apart from cotton.

Chemically, jute fibers or stands contain a higher content of lignin and a lower content of cellulose than any other commercial bast fiber, the chemical analysis of a typical fiber showing 24.41 percent by weight of lignin and 63.24 percent by weight of cellulose, which composition results in a fiber lacking in strength and durability. Being inexpensive, jute is extensively used for burlap, sacking, backing for linoleum and rugs, webbing, twine, and in a variety of products where low cost is more important than strength or durability. Because of their high lignin content, jute fibers generally possess a color ranging from reddish-brown to yellowish-brown, and change to a dingy brown upon aging or prolonged exposure to light. Since the natural color of jute is somewhat unattractive, most jute fabrics are bleached prior to dyeing. When jute fabrics are bleached in accordance with conventional bleaching techniques, even these bleached jute fabrics, however, show a pronounced tendency to darken, or revert to a brownish color, upon aging or exposure to light. Notwithstanding their inexpensiveness, the poor colorfastness of jute fabrics have precluded more extensive utilization of these fabrics.

Using an aqueous bleaching solution containing potassium permanganate and phosphoric acid we have found that when the ratio of potassium permanganate to phOsphoric acid in this aqueous bleaching solution is carefully adjusted so that it is within the range from about 1:0.7 to about 1:1.1 and jute fabrics are bleached at a tempera ture from about 60 F. to about 110 F. and at a pH below 3.0, after which the bleached jute fabric must then be scavenged by treatment with an inorganic reducing rates Patent ice agent at a pH below 4.0, it is possible to produce a lightfast jute fabric having a colorfastness appreciably greater than that of any jute fabric bleached by conventional techniques. As used herein, the term jute denotes any bast fibers or strands produced from the herbaceous annual plant Corchorus, or any other bast fibers or strands containing a relatively high lignin content.

Based on this discovery, the invention provides an improved process for producing lightfast jute which comprises (a) bleaching a jute fabric by treating the fabric with an aqueous bleaching solution containing potassium permanganate and phosphoric acid at a temperature in the range from about 60 F. to about 110 F. and at a pH below 3.0, the ratio of potassium permanganate to phosphoric acid in the aqueous bleaching solution being in the range between about 1:0.7 to about 1:1.1, and (b) scavenging the bleached jute fabric by treating the bleached fabric with an aqueous solution of an inorganic reducing agent at a pH below 4.0, thereby forming a lightfast jute fabric. Lightfast jute fabrics produced in accordance with the process of the invention possess a colorfastness equal to not less than 25 Standard Fastness Hours (and in most instances from 30 to 40 Standard Fa tness Hours), as determined by AATCC Standard Test Method 16A-1963, with no progressive shade change thereafter. By way of comparison, jute fabrics which had been bleached by conventional techniques possess a colorfast ness of only 5 Standard Fading Hours before the fabric undergoes a shade change after exposure to a standard light source.

To produce lightfast jute in accordance with the process of the invention, a jute fabric is treated in an aqueous bleaching solution containing potassium permanganate and phosphoric acid at a temperature in the range from about 60 F. to about 110 F. and at a pH below 3.0. There appears to be some synergistic effect between potassium permanganate and phosphoric acid in the aqueous bleaching solution, since neither the use of other alkali metal permanganates with phosphoric acid nor the use of potassium permanganate with other inorganic acids function as effectively as the combination of potassium permanganate and phosphoric acid to bleach the jute fabric.

The concentration of the aqueous bleaching solution used to bleach the jute fabric preferably should contain from about 3 to about 15 percent by weight of potassium permanganate and from about 2 to about 17 percent by weight of phosphoric acid (calculated on the basis of 100% H PO or from about 3 to about 22.5 percent by weight of H PO all percentages except those designating the phosphoric acid strength being based on the Weight of the fabric being treated. The aqueous bleaching solution is effective for the purposes of the process of this invention only when the ratio of potassium perman ganate to phosphoric acid (basis H PO is in the range between about 1:0.7 and about 121.1, or on the basis of 75% strength H PO in the range between about 1:1 to about 111.5, and the pH of the solution is below 3.0, for any variation of these reaction conditions adversely affect the colorfastness of the fabric.

The jute fabric is immersed in the aqueous bleaching solution until the jute is completely bleached or the potassium permanganate completely reduced. Depending on the concentration of potassium permanganate and phosphoric acid employed in the aqueous bleaching solution, the jute fabric will be bleached for a period from about 20 minutes to about 1 hour, although these time periods are not as critical to the process as the pH of the aqueous bleaching solution and the ratio of potassium permanganate to phosphoric acid in the bleaching bath.

Upo-n removal of the bleached jute fabric from the aqueous bleaching solution, the fabric is then scavenged by immersion in an aqueous solution containing an inorganic reducing agent, preferably sodium bisulfite. at a. temperature in the range from about 80 F. to about 160 F.v and :at a pH below 4.0. Although any acid may be used to adjust the pH of the scavenger solution, outstanding results have been obtained using phosphoric acid in this solution. Preferably, the scavenger solution should contain from about 4 to about 22 percent by weight of sodium bisulfite, based on the weight of the fabric being treated, and sufiicient phosphoric acid (generally from. 40 to 60 percent by weight of the sodium bisulfite of 75 H PO to lower the pH to below 4.0.

After the bleached jute fabric has been scavenged by immersion in the aqueous scavenger solution, the fabric should be scoured or washed with hot water containing a surfactant until the fabric is free from any residual odor of bisulfite, following which it may be soured with acetic acid prior to drying.

Jute fabrics which have been finished in accordance with the process of the invention are characterized by a colorfastness equal to not less than 25 Standard Fading Hours, and in most instances between 30 and 40 Standard Fading Hours, as determined by AATCC Standard Test Method 16A-1963, with no progressive shade change thereafter. Using the International Geometric Gray Scale, on which a Class 4 fastness rating indicates just appreciable fading of a test specimen or standard, AATCC Standard Test Method l6A-1963 measures the number of hours required to produce just appreciable fading (Class 4 on the Gray Scale) when the test specimen is exposed to a specified calibrated carbon-arc light source under specified conditions. The number of hours of exposure required under these conditions to produce just appreciable fading are designated as Standard Fading Hours, which is a measure of the color-fastness of the fabric. By way of comparison, jute fabrics which had been bleached by conventional techniques undergo a Class 4 shade change after Standard Fading Hours, and continue to darken even further on prolonged exposure to light or aging.

The following example is illustrative of the ease with which jute may be made lightfast in accordance with the process vof the invention;

A coarsely woven jute fabric, identical to the unbleached greige fabric sold commercially, was bleached in an aqueous bleaching solution containing 10 percent. by weight of potassium permanganate and 12 percent by weight of 75% phosphoric acid, both percentages being based upon the weight of the fabric being treated. The fabric was immersed in the bleaching solution at a tem-- perature of about 65 F. for approximately 45' minutes, after which the fabric was washed in cold water until the rinse Water was clear and then washed in hot water (140 F.) until the rinse water was clear.

The bleached jute fabric was then immersed in an aqueous solution containing 10 percent by weight of so dium bisulfite and 5 percent by weight of 75% phosphoric acid, both percetanges being based on the weight of the fabric. The temperature of this bisulfite scavenger solu tion was kept at about 120 F., and the fabric treated in this manner for approximately 45 minutes.

The fabric was then removed from the bisulfite scavenger solution, washed for 10 minutes with hot water (140160 F.), and thenscoured .for an additional 10 minutes with hot. water (180-190 F.) containing 0.5 percent by weight of a nonionic surfactant (Triton X400, which is an alkyl aryl polyether alcohol). The fabric was then rinsed with water until no residual bisulfite odor remained and then soured with 2 percent by weight of acetic acid which, after rinsing, left the fabric with a of about 6.0. After drying, the fabric had a. very attractive white finish.

Exposure of the finished jute fabric to the FadeOmeteJk apparatus showed that a. Class 4 Gray Scale) shade change occured between 30 and 40 hours of continued exposure, with no progressive shade changes even after hours of continued exposure, following which the test was discontinued.

We claim:

1. The process for producing lightfast jute which comprises (a) bleaching a jute fabric by treating the fabric with an aqueous bleaching solution consisting essentially of potassium permanganate and phosphoric acid at a temperature in the range from about F. to about 110 F. and at a pH below 3.0, the ratio of potassium permanganate to phosphoric acid in the aqueous bleaching solution being in the range between about 1:0.7 to about 121.1, (b) scavenging the bleached jute fabric by treating the bleached fabric with an aqueous solution of soduim bisulfite at a pH below 4.0, and (c) scouring the scavenged, bleached fabric by washing it with an queous solution of water-soluble surfactant, thereby forming a. light-fast jute fabric.

2. The process for producing lightfast jute which comprises (a) bleaching a jute fabric by treating the fabric with an aqueous bleaching solution consisting essentially of potassium permanganate and phosphoric acid at a temperature in the range from about 60 F. to about 110 F. and at a pH below 3.0, the ratio of potassium permanganate to phosphoric acid in the aqueous bleaching solution being in the range between about 1:0.7 to about 1:1.1, (b) scavenging the bleached jute fabric by treating the bleached fabric with an aqueous solution of sodium bisulfite at a temperature in the range from about F. to about 160 F. and at a pH below 4.0, and (c) scouring the scavenged, bleached fabric by washing it with an aqueous solution of a water-soluble surfactant, thereby forming a lightfast jute fabric.

3. The process for producing lightfast jute which comprises (a) bleaching a jute fabric by treating the fabric with an aqueous bleaching solution consisting essentially of from about 3 to about 15 percent by weight of potassium permanganate and from about 2 to about 17 percent by weight of phosphoric acid at a temperature in the range from about 60 F. to about F. and at a pH below 3.0, the ratio of potassium permanganate to phosphoric acid in the aqueous bleaching solution being in the range between about 1:0.7 to about 111.1, (b) scavenging the bleached jute fabric by treating the bleached fabric with an equeous solution containing from about 4 to about 22 percent by weight of sodium bisulfite at a temperature in the range from about 80 F. to about F. and at a pH below 4.0, and (c) scouring the scavenged, bleached fabric by washing it with an aqueous solution of a water-soluble surfactant, thereby forming a lightfast jute fabric, all percentages being based upon the weight of the fabric being treated.

4. The process for producing lightfast jute which comprises (a) bleaching a jute fabric by treating the fabric with an aqueous bleaching solution consisting essentially of from about 3 to about 15 percent by weight of potassium permanganate and from about 2 to about: 1.7 percent by weight of phosphoric acid for a period from about 20 minutes to about 1 hour at a temperature in the range from about 60 F to about 110 F. and at a. pH below 3.0, the ratio of potassium permanganate to phosphoric acid in the aqueous bleaching solution being in the range between about 1:0.7 to about 111.1, (b) scavenging the bleached jute fabric by treating the bleached fabric with an aqueous solution containing from about 4 to about '22 percent by weight of sodium bisulfite for a period from about 30 minutes to about 1 hour at a temperature in the range from about 80 F. to about 160 F. and at a pH below 4.0, and (c) scouring the scavenged, bleached fabric by washing it with a hot aqueous solution of a water-soluble surfactant, and then rinsing the scoured fabric to remove any residual bisulfite odor, there-by forming a lightfast jute fabric having a color-fastness equal. to from 30 o 0 Standard Fastness Hours, as de termined by AATCC Standard Test. Method 1618-1963, all percentages being based upon the Weight of the fabric being treated,

5. A lightfast jute fabric having a colorfastness equal to not less than Standard Fastness Hours, as determined by AATCC Standard Test Method 16A-1963, and produced by (a) bleaching a jute fabric by treating the fabric with an aqueous bleaching solution consisting essentially of potassium permanganate and phosphoric acid at a temperature in the range from about F, to about F. and at a pH below 3.0, the ratio of potassium permanganate to phosphoric acid in the aqueous bleaching solution being in the range between about 1:0.7 to about 121.1, (b) scavenging the bleached jute fabric by treating the bleached fabric with an aqueous solution of sodium bisulfite at a temperature in the range from a-bout"80 F, to about F. and at a pH below 4.0, and (c) scouring the scavenged, bleached fabric by Washing it with an aqueous solution of a water-soluble surfactant,

, 6 6. A lightfast jute fabric according to claim 5, in which the colorfastness is equal to from 30 to 40 Standard Fastness Hours, as determined by AATCC Standard Test Method 16A-1963, "with no progressive shade change thereafter,

References Cited UNITED STATES PATENTS 534,450 2/1895 Clapham 8-111 10 1,032,151 7/1912 Maupai mmwmuuu. 8-111 1,991,335 2/1935 Reddish 8-111 FOREIGN PATENTS 23,745 1912 Great Britain, 15 826,190 12/1959 Great Britainl LEON D. ROSDOL, Primary Examinera M. WEINBLATT, Examiner, 

